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Danver had built the car himself and was in the process of using it to be the first one to do so. However, The Leader was also in the race to do so and had hoped to use the acquired fame to launch his brand globally. When The Leader failed to convince Danver to pilot Leader's own Mach 1 car, The World Leader, he used violence and extortion to keep Danver away from achieving his goal. When Chuck failed to comply, Leader sent an associate who proceeded to incapacitate Chuck, thus making sure he would not be fit in time for the world record. Chuck, afraid of what The Leader might do to his sisters, told no one of this encounter and just attributed his damaged leg to falling. He subsequently left the Sonic Bird project alone.

After a three week hiatus, Danver's sister Helen sent a telegram to Steve Warson out of her brother's name, requesting his help. Steve then asks for the help of Michel Vaillant in getting the Sonic Bird done on time, before rain season starts.

A few days after this decision, Steve Warson successful tests the Sonic Bird to ensure it's supersonic capabilities, reaching 770 miles per hour. Though a Leader pilot tried to smash The World Leader into the Sonic Bird for disobeying Leader, Steve managed to safely pilot the car away. A few weeks later, Chuck, now fully healed, pilots the Sonic Bird to an official world record amidst massive public interest. This success also paves the way for Chuck Danver to enter races with the Vaillante team.

Though the comic presents a fantastic story on breaking the sounds barrier in 1968, it would take another 29 years for a car to actually cross this mythical barrier. On October 17th, 1997, the ThrustSSC became the first car to break the speed of sound for land vehicles.